I cover my grey and my sun conure at night, always have, I think they prefer it that way and I never hear a peep out of either one of them. I use a black sheet I bought at Walmart, the flat one and it works just fine, no need for the fancy ones that cost a bundle.
When you are gone during the day and your grey feels like taking a nap, he or she will do just that.
Ask all the questions you want, how else are you going to learn the answers unless you ask.